Solar heat collectors typically incorporate a collector, a circulating fluid medium, and a means for transfering heat from the collector to the circulating fluid medium. These collectors are characterized by three deficiencies. First, efficiency is low because of the necessity of a heat exchanger to transfer heat from the collector to the circulating fluid medium. Second, heat exchangers typically involve complex manifolding and fluid circulation paths which result in undesirably high operating pressures within the heat exchanger. Third, the collectors operate at high temperatures, and in the event of a circulation failure, even higher stagnation temperatures. The high pressure and high temperature characteristics of prior art solar heat collectors require the use of expensive materials and construction techniques to produce collectors capable of withstanding the high pressure and temperature conditions.
The present invention eliminates the need for a heat exchanger in the solar heat collector by utilizing a circulating absorptive fluid medium to absorb solar energy directly. A cascaded reservoir arrangement permits the collector to efficiently capture the energy impinging the surface area of the collector while simultaneously requiring only a minimal fluid pressure within the collector. The transparent reservoirs operate at a temperature no higher than that of the circulating fluid, and a self-draining feature is active during a stagnant conditon so that in the event of a circulation failure the absorptive fluid medium automatically drains from the collector leaving the collector non-absorptive, and thus with a low stagnation temperature. These characteristics of the present invention allow for the use of inexpensive materials and construction techniques in the construction of durable solar heat collectors.